Tragacanth, viscosity

Other thickeners used include derivatives of ceUulose such as methylceUulose, hydroxypropylmethylceUulose, and ceUulose gum natural gums such as tragacanth and xanthan (see Cellulose ethers Gums) the carboxyvinyl polymers and the poly(vinyl alcohol)s. The magnesium aluminum siHcates, glycol stearates, and fatty alcohols in shampoos also can affect viscosity. 

The viscosity of natural gums, such as cellulose gums, mannogalactans, seaweed, pectin, locust bean gum, guar gum, and tragacanth has important industrial applications in the food, pharmaceutical, cosmetic, textile, adhesives, and paint fields. The characteristics of viscosity are related to specific uses and to the economics of the process. 

Hand lotions, of the emulsion type, are also, in most cases, oil in water emulsions. A true emulsifying agent is usually used to form the emulsion and for cleansing properties. Vegetable gums, like tragacanth or Irish moss extract, are added, not only to stabilize the emulsion but to increase the emollient properties, because of the added viscosity effect. 

Flavor emulsions are similarly stabilized by the viscosity produced upon addition of a vegetable gum, such as tragacanth, Irish moss extract, arabic, a cellulose gum, or one of the alginates, to the aqueous phase. Here the oil phase, in the form of the flavor, is in small proportion to the water. In the absence of the acetic acid, contained in the vinegar of the French dressing. 

Tragacanth is widely used as a natural emulsifier in conjunction with acacia and is an effective viscosity modifier for suspension formulations. It contains a variety of methoxylated acids that upon contact with water become a gel. At around pH 5, it renders the maximum stable viscosity due to aging even though the maximum viscosity occurs at pH 8 with the freshly prepared solution. 

It is an effective suspending agent for pharmaceuticals and is used in conjunction with acacia as an emulsifier, the tragacanth imparting a high stmctural viscosity while the gum arabic adsorbs at the oil/water interface. It is also used in spermicidal jellies, acting by immobilising spermatozoa and as a viscous barrier. 

Maximum initial viscosity of solns at pH 8 maximum stable viscosity near pH 3. Forms a deep yellow stringy precipitate when a soln is boiled with a few drops of 10% aqueous ferric chloride soln. A stringy precipitate formed also on heating a soln with Schweitzer reagent. Tragacanth is entirely insol in alcohol. 

Viscosity is possibly the most important single consideration for evaluating gum tragacanth. It can be called a yardstick for judging quality and serves as a guide to its behavior as a suspending agent, stabilizer, or emulsifier (16, 17). 

Table III illustrates the variation in viscosity encountered in commercial powdered tragacanth. Results are expressed in seconds time of flow through a Dudley pipet at room temperature and at the concentration indicated.

The high viscosity of tragacanth solutions makes it useful in pharmaceutical practice as a suspending agent in aqueous mixtures containing resinous tinctures (such as jalap and myrrh) and heavy insoluble powders. Glycerite of tragacanth is a useful excipient to bind pill masses. 

It all depends upon the purpose for which they are to be used, whether in pharmaceutical preparations or for industrial uses. Usually solutions of tragacanth made in the cold (room temperature) are better. They are allowed to stand until completely hydrated and reach maximum viscosity. Solutions for viscosity determinations, as we do them routinely (usually by the pipet method) are made in either 0.5 or 1% concentrations and shaken for 2 hours on the day prepared. Then they are allowed to stand and shaken again the next day, after which they are permitted to age for 1 or 2 hours before the viscosity is taken. As far as emulsification is concerned, it doesn t make too much difference how the solutions are prepared. As far as I know the solutions are made cold. I do not think they are heated for emulsification ... 

These gums are natural products and are produced under conditions of climate and so on which may vary from year to year or from location to location. Any given lot produces a viscosity that is inherent in that particular lot. What can be done, of course, is a general standardization of gum tragacanth for specific needs of the trade. It is necessary to know the customer s requirements in order to select the grade but it naturally increases the production cost to do that. 

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